Google Webmaster tools "Time spent downloading a page"

Question

In Google Webmaster Tools -> Diagnostics -> Crawl Stats, there is a chart Time spent downloading a page (in milliseconds).

What is that chart measuring?

Is it the time to fetch the HTML text only, or does it include the time to fetch other files included in the head section of the HTML text, or maybe it's the overall time to load the whole page including embedded widgets and ads?

I can't find any clues in the Google Help.

Answer 1

From Google:

Time spent downloading a page (in Crawl stats) is the time for just downloading the HTML of your page, by Googlebot. Site Performance, on the other hand, shows you how long it took to load a full page (including all its images, scripts, etc), by your website's users across the globe.